1. Field of the Invention
The present invention relates to a light emitting device.
2. Description of the Related Art
In recent years, various light emitting devices such as light emitting diode (LED) and laser diode (LD) apparatus that employ high output semiconductor light emitting elements (also referred to below simply as light emitting elements) have been developed.
Recently, an assortment of electronic components have been proposed and developed, and demands on their performance has also increased. In particular, long-term, stable performance is demanded even in harsh operating environments. Similarly, for light emitting devices beginning with light emitting diodes, performance demands in fields such as general lighting and automotive lighting are increasing daily, and high output and high reliability are particularly in demand. Furthermore, supply of these devices at low prices while maximizing their performance is required.
In general, a light emitting device has a substrate that carries electronic components such as semiconductor light emitting elements (also referred to below as light emitting elements) and protection devices, and conducting material to supply electrical power to those electronic components. Further, the light emitting device has light-transparent encapsulating material to protect the electronic components from the outside environment.
To achieve high output, the output of the employed light emitting elements themselves can be increased. In addition, it is effective to improve the light extraction efficiency via the materials and configuration of components such as the substrate, the conducting material, and the encapsulating material.
For example, high conductivity metals are used as the conducting material, and the surface of the conducting material can be plated with silver to efficiently reflect light from the light emitting elements. Further, resin that easily passes light from the light emitting elements is appropriate as the encapsulating material. Among those resins, silicone resin, which has excellent heat durability and is able to withstand harsh environments (weather-ability), can be used in an effort to increase apparatus lifetime.
However, silver has the tendency to degrade easily due to atmospheric constituents such as sulfur. Accordingly, Japanese Laid-Open Patent Publication No. 2004-207258A discloses use of an organic agent to prevent silver discoloration. In addition, Japanese Laid-Open Patent Publication No. 2006-303069A discloses plating the silver with a noble metal, and Japanese Laid-Open Patent Publication No. 2007-324256A discloses a sol-gel glass coating.
In addition, light emitting devices that carry not only light emitting elements, but also carry electronic components such as Zener diodes or submounts have been developed. As a result, high reliability, long lifetime light emitting devices are possible. Since these other types of electronic components can easily absorb light from the light emitting elements, a reflective layer can be provided that covers those components and reduces light loss (see for example, Japanese Laid-Open Patent Publication No. 2005-26401A).
However, in the case of organic material covering silver, environmental resistance is problematic and the system can easily degrade over time. For noble metal plating, although environmental resistance is not a problem, noble metals have lower reflectance than silver and initial reduction in output is unavoidable.
Further, the thickness of sol-gel glass coating is difficult to control, mass production is problematic, and as a result cost is an obstacle.